as Gazza notes, all kinds of different factors can make a number feel good to play, and a lot of the factors are real variable: what the band (collectively, individually) feels up to - getting into a groove - pacing the show and themselves - promoting an album - audience expectations/reactions - the pursuit of a musical challenge like ... oh say like a three-way harmony between two singers and a pedal steel.
like TD, YGMR pretty clearly just plain feels good to play.
"What do you want - what?!"
- Keith